Inside the Hawaiian seed bank figuring out how to store the rarest seeds on Earth

Visits to the seed bank at the National Tropical Botanical Garden begin with removing your shoes. The seed bank, on the Hawaiian island of Kaua’i, is housed alongside NTBG’s collection of 80,000 dried plant specimens and rare botany books in a building that can withstand Category 5 hurricanes. It does have a vulnerability, though: pests. Funguses or bugs — like booklice — hiding in a visitor’s soles could threaten the collections. For the same reason, anything that’s brought into the building — office supplies, furniture, books — is frozen for two weeks.

To the right of the foyer, where shoes are lined up against the wall, there’s a wooden door leading to room 116: the seed bank and laboratory. It’s a single nondescript room: one side is lined with long tables filled with lamps, trays, and machines; the other is lined with freezers. But this unassuming lab has a remarkable job: if Hawaii’s rare plants — some of the rarest in the world — stand a chance for survival, it’ll be because of the 3 million seeds stored here.

Hawaii has lost over 130 plant species since it was first inhabited, and today, it’s home to more than 40 percent of all endangered and threatened plant species in the US. That’s because Hawaii is an island ecosystem, where plant species have evolved for millions of years in isolation. These plants are extremely vulnerable — all that time they spent cut off from the rest of the world meant that they shed defense mechanisms or simply didn’t develop them. But when people came — first from Polynesia, now from all over the world — they brought weeds and animals against which the native plants are defenseless.

Dustin Wolkis, NTBG’s seed bank manager.

Seeds in a petri dish placed inside the germination chamber.

“Right now in the state, we’re in crisis mode,” says Dustin Wolkis, NTBG’s seed bank manager. “We’re losing species right in front of our eyes.”

Some species — like the native Kadua haupuensis, which has been ravaged by invasive pigs and goats — are thought to be extinct in the wild. But their seeds are safely stored at NTBG. If one day habitats are restored or managed so that invasive species are not a threat, these seeds could be replanted in the wild — even bringing some plants back from extinction. That’s where the seeds will play a role. (Of the 3 million seeds in the collection, 97 percent are from native Hawaiian plants.)

In the meantime, the seeds aren’t just sitting on the shelf doing nothing — they’re sprouted and grown into plants, from which new seeds are collected. That process means that the seeds at NTBG can be studied. Scientists are finding out the best ways to store them, and how long they can stay in stasis before dying. “Seeds are living things and they have an expiration date just like all other living things,” Wolkis says. “It’s my job to figure out what that expiration date is and push back.”

One of NTBG’s nurseries.

The seeds are collected by NTBG’s volunteers and botanists, who are known for rappelling from ridges and jumping off helicopters to reach Hawaii’s rarest plants in remote locations. When the seeds are brought in from the field, Wolkis and his team get to work to understand what kind of seed it is, and how it should be stored. (This depends on the number of seeds the bank has; if the bank receives fewer than 100 seeds of one species, no testing is done.) “It’s different for every species,” he says. To determine that, the lab analyzes the seeds to understand how much moisture they have, and then the seeds are dried just a little. Next, the seeds are put on a petri dish and placed inside a machine that looks like a fridge that allows researchers to control for temperature, as well as alternate between “light” and “darkness.” It’s called a germination chamber; seeds are left in there to see if a little root comes out of them, which means the seeds are alive.

If the seeds sprout, some more seeds of the same species are then dried a little bit more, and put in the germination chamber again. This is a process that’s repeated a few times to determine how much drying the seed can withstand. Drying is one way to extend a seed’s shelf life. Then, Wolkis tests if the seeds can survive sub-freezing temperatures, since cooling a seed is the other main way to push its expiration date. The seeds are sealed inside a square aluminum foil pack and put at negative 4 degrees Fahrenheit for three months. Then, it’s time to go into the germination chamber again, to check if the seeds are still alive. Seeds that survive this temperature and level of drying are hardy — like legumes, or possibly the seeds of the Ohiʻa tree, a native Hawaiian plant that has beautiful red, yellow, or orange flowers. Other seeds are more frail, and die when dried or frozen. Knowing which seeds are which is, of course, is crucial for preservation.

Clockwise from top: the native Hawaiian Ohiʻa tree; seedlings at the nursery; one of NTBG’s nurseries in Kaua’i.

The seedlings coming out of the germination chamber aren’t thrown out. Instead, they’re given to NTBG’s nurseries, where they’re planted and grown into plants. New seeds are then collected and stored in the bank — so the collection can be freshened up. “People think that I’m in the business of acquiring seeds and I totally am, but I’m also in the business of withdrawing seeds,” Wolkis says.

Once Wolkis determines what kind of seed he’s dealing with — and decides whether to store it at negative 4 degrees Fahrenheit or negative 112 degrees Fahrenheit — the seeds are taken out of the freezer and into the germination chamber after one year. Then, generally, the seeds are tested again after two years, five years, 10 years, and then every 10 years after that — though the process may vary, depending on how many seeds the bank has. It’s an unending process that’s allowing Wolkis to really understand how far these seeds can go, to make sure they’re still alive when they’ll be needed to replant Hawaii’s forests. After all, if you’re storing seeds of species that might have already gone extinct in the wild, you want to make sure the seeds are still viable.

Some of the plants grown at the nursery are planted at NTBG’s 1,000-acre Limahuli preserve.

Next, Wolkis is going to experiment with liquid nitrogen, which is negative 321 degrees Fahrenheit. That’s so cold that the moisture in the seed freezes so rapidly that it doesn’t leave time for ice crystals to form. That’s good news because ice crystals are lethal to cells. Using liquid nitrogen could be the solution to storing particularly frail seeds that can’t withstand freezing at higher temperatures. The first seeds to get the liquid nitrogen treatment will be those of the critically endangered native plant Phyllostegia electra.

Maybe if Wolkis succeeds, its seeds will be safely stored for many years to come — until it’s time to replant them, allowing the plant’s elongated white flowers to dot Hawaii’s forests once again.